Copy-protected data carrier

ABSTRACT

The present invention relates to a data carrier comprising an information layer (1) itself comprising a specific area ( 4 ) able to deliver a first optical signal and a second optical signal when illuminated by a light source. Said data carrier also comprises an additional layer ( 2 ) able to deliver an electrical signal when illuminated by the second optical signal, said electrical signal corresponding to a predetermined pattern. The combination of the first optical signal and of the electrical signal forms a cryptographic key that is required to decrypt encrypted data contained in the information layer. This invention is particularly relevant to the read out of data stored on optical discs of the Read Only Memory type.

FIELD OF THE INVENTION

The present invention relates to a data carrier.

The present invention also relates to a method of and a device forreading such a data carrier.

This invention is particularly relevant to the read out of data storedon optical discs, such as Small Factor Format Optical SFFO discs orBlu-ray discs, of the Read Only Memory ROM type or the like.

BACKGROUND OF THE INVENTION

Up to now, it is relatively easy to make a copy identical to an originaldata carrier, and more especially to an original optical data carrier,simply by using replication techniques.

Counterfeit copying of such an optical data carrier has become asignificant problem, resulting in less royalty income for license ownersof a technology as well as for content distributors.

Several methods for preventing said copies have already been implementedFor example, the international patent application WO 00/14734 disclosesan optical data carrier containing primary data as well as security datain two separated layers. In this application, a beam of radiation isdirected toward a data storage surface of the optical data carrier andreflected signals are converted into electrical signals. Said signalsare processed to ascertain the presence of the primary data and thesecurity data carried by the optical data carrier. Typically, an outputis permitted to output the primary data only upon detection ofappropriate security data.

According to this prior art, the read out of data is made optically, andthe reflected optical signals are converted into electrical signalsoutside the optical data carrier. As a consequence, this solution israther complex and expensive, as it needs a specific module for theconversion of an optical signal into an electrical signal. Moreover,said solution is not fully satisfactory as a hacker may have access tothe security data and thus a counterfeit copy is still possible althoughsuch a copy may be difficult to achieve.

SUMMARY OF THE INVENTION

It is an object of the invention to propose a data carrier that is lesscomplex and more difficult to copy than the solution of the prior art.

To this end, the data carrier in accordance with the invention comprisesan information layer comprising a specific area able to deliver a firstoptical signal and a second optical signal when illuminated by a lightsource, and a patterned additional layer able to deliver an electricalsignal when illuminated by the second optical signal, said electricalsignal corresponding to a predetermined pattern, the combination of thefirst optical signal and of the electrical signal forming acryptographic key that is required to decrypt encrypted data containedin the information layer.

The present invention is based on the photoelectric or an equivalenteffect. It is a hardware related solution, which is rather efficient toprevent illegal copying. As a matter of fact, the combination of theelectrical signal and of the optical signal provides a completecryptographic key that is required to get access to die data containedin the carrier. It is then very difficult for a hacker to copy theelectrical signal onto an illegally replicated disc. And without saidelectrical signal, the cryptographic key can not be derived and, as aconsequence, an illegally replicated disc containing only the opticalsignal can not be read out and is therefore useless. Moreover, a datacarrier in accordance with the invention is both easy and cheap tomanufacture.

According to an embodiment of the invention, the predetermined patternis obtained from a segmentation of the additional layer in activated anddeactivated areas. According to another embodiment, the additional layercomprises electrodes, one of which being segmented in order to obtainthe predetermined pattern. According to another embodiment, the specificarea is contained in the initialization area of the information layer.The additional layer may be a thermoelectric layer or a photoelectriclayer. Said photoelectric layer can be made of amorphous silicon or ofphotoelectric tungsten disulfide.

The present invention also extends to a method of and device for readingsuch a data carrier. Said device for reading comprises means for readingthe first optical signal delivered y the specific area of theinformation layer, means for reading the electrical signal delivered ythe additional layer, means for computing a cryptographic key from acombination of the first optical signal and the electrical signal, andmeans for decrypting encrypted data contained in the data carrier fromthe cryptographic key.

The present invention also extends to a method of and device forrecording information on such a data carrier. Said device for recordingcomprises means for reading the first optical signal delivered by thespecific area of the information layer, means for reading he electricalsignal delivered by the additional layer, means for computing acryptographic key from a combination of the first optical signal and theelectrical signal, means for encrypting information based on thecryptographic key, and means for storing the encrypted information onthe data carrier.

These and other aspects of the present invention will be apparent from,and elucidated with reference to, the embodiment described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way ofexample, with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic perspective view of an embodiment of a datacarrier in accordance with the invention,

FIG. 2 is a schematic view of a section of an embodiment of a datacarrier in accordance with the invention,

FIG. 3 is a more detailed section view of the data carrier of FIG. 2 inaccordance with the invention, and

FIG. 4 shows the chemical reaction illustrating a photo-oxidation of apolymer for manufacturing a data carrier in accordance with theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is depicted in the following description in thecase of an optical disc but it will be apparent to a person skilled inthe art that the present invention is also applicable to other type ofdata carriers, such as, for example, magnetic disks.

The optical disc is, for example, of the ROM type. The invention isparticularly useful in this case as it can prevent from mass copying thecontent of said ROM discs. However, it will be apparent to a personskilled in the art that the present invention stays applicable for othertypes of optical discs, for example of the rewritable RW type or of thewrite once R type, for which a user can decide to protect their personaldata from being copied.

A conventional optical disc comprises a standard information layercomprising multimedia data such as text, audio or video. Such aconventional optical disc is not protected against illegal copying ofsaid data. The present invention aims at proposing an easy and cheapsolution for preventing this illegal copying.

To this end, said invention proposes to equip the new disc generationfor optical data storage, such as Small Factor Format Optical SFFO discsor Blu-ray discs, with a patterned additional layer able to deliver anelectrical signal when illuminated by an optical signal. Said additionallayer is based on the photoelectric effect as described in the followingdescription, or on the thermoelectric effect or any other suitableeffect. In the case where the thermoelectric effect is utilized, thethermo-current generated by heat caused by irradiation of the lightsource is detected in the same manner as described below.

FIG. 1 gives a schematic perspective view of an embodiment of a datacarrier in accordance with the invention.

The optical disc 10 comprises an information layer 1 able to deliver anoptical signal. The optical signal is read out, for example from top, byan optical pick up unit OPU (not shown). In the present invention, theinformation layer comprises, for example, data content encryptedaccording to a predetermined cryptographic key.

It also comprises a photoelectric layer 2. This additional layer workson the basis of the photoelectric effect providing an electrical signalwhen illuminated by a light source such as a laser. The electricalsignal is intended to be read out in a specific device in accordancewith the invention, as described hereinafter. Said photoelectric layercan be an internal layer as shown on FIG. 1, or an external layeropposite to the information layer.

The rotation axis 3 of the disc corresponds to a hole in the disc. Aspecific area 4 of the information layer I is used for a modulation ofthe optical signal reaching the photoelectric layer 2. The specific areais, for example, the initialization area of the optical disc (i.e. thearea of the disc that is read when the disc is inserted in the opticaldisc drive).

The modulated electrical signal combined with the optical signal takinginto account their relative time behavior make the predeterminedcryptographic key that gives access to the content of the optical disc.

It is relatively easy to read out this electrical signal together withthe corresponding disc information But for a hacker, it is verydifficult to copy this electrical signal onto another disc and apotential end-user of such a replicated disc needs this signal to readout the content of the disc. Moreover, reverse engineering is notpossible, as it will destroy the information.

FIG. 2 gives a schematic view of a section of an embodiment of a datacarrier in accordance with the invention.

An optical disc player must be able to read out the electrical signal 9delivered by the photoelectric layer. For that purpose, some electrodesare required. The optical disc comprises an upper electrode 5, whichneeds to be transparent for the laser light. Said electrode is made of,for example, Indium Tin Oxide ITO films. Said disc also comprises alower electrode 6, for example in Al, preferably coated with a low workfunction material such as LiF or CaF. The optical pick up unit OPUcomprises here a laser 7 focused in the information layer.

FIG. 3 describes in more detail an embodiment of the data carrier ofFIG. 2.

Said optical disc comprises the specific area 4 of the information layer1, for generating a reflected 4a and transmitted 4b optical signal, oneof which being the reference optical signal 8. The form of saidreference optical signal 8 depends on the structure of the specific area4 of the information layer 1 as shown in FIG. 3. Said structure isadapted either to reflect R or to transmit T the light delivered by thelight source.

The optical disc comprises the photoelectric layer 2 able to deliver theelectrical signal 9 corresponding to a predetermined pattern, whenilluminated by the signal from the information layer that does not formthe optical signal.

According to a first embodiment of the invention, the photoelectriclayer 2 is patterned using a segmental activating or deactivating ofsaid layer. Thanks to this segmentation the electrical signal 9corresponding to the predetermined pattern is generated when illuminatedwith an optical signal.

The predetermined pattern can be written in the photoelectric layer, forexample during manufacturing of the disc by patterned UV irradiation inan oxygen environment. FIG. 4 shows the chemical reaction of thatprocess, which is also called bleaching. Such a photo-oxidation of thepolymer can locally destroy or deactivate the polymer. This results in alocally high-ohmic behavior, which does not give rise to anyphotocurrent under radiation.

Alternatively, the electrodes could also be patterned. For instance,thin metal films on silicon could be used, acting as metallicelectrodes. After a local heating or after an irradiation, silicides areformed. Said silicides are typically defined by high-ohmic orsemi-conducting behavior. Another way is to generate pinholes in eitherthe upper or the lower electrode, for example usingpoly(3,4-éthylènedioxythiophène) PEDOT electrode which are easy toconfigure.

According to another embodiment, the two above-described embodiments canbe combined, that it to say the photoelectric layer 2 is segmented inactivated 2 a and deactivated 2 b areas and one electrode is segmentedin segments 6 a and 6 b. FIG. 3 shows the electrical signal 9 resultingfrom such a combination.

In the example of FIG. 3, the reference optical signal 8 is thereflected signal 4 a and the electrical signal 9 is obtained from thetransmitted signal 4 b. Nevertheless, it will be apparent to a personskilled in the art that it is also possible to read the referenceoptical signal in a transmission configuration, i.e. the referenceoptical signal 8 is the transmitted signal 4 b, while detecting thephotoelectric signal in reflection, i.e. the electrical signal 9 isobtained from the reflected signal 4 a.

The photoelectric layer can be made of existing materials and stackcombinations used in solar cells, for instance amorphous silicon asdescribed by I. Garner in “Communications-International”, vol. 16, no. 3(1989) 73.

It can also be made of photoelectric tungsten disulfide WS₂ as describedin “Solar Energy Materials & Solar Cells”, by C. Balif, M. Regula, F.Levy, 57 (1999) 189, of copper, indium or gallium selenide, cadmiumdisulfide, cadmium diselenide, gallium arsenide, aluminum galliumarsenide.

The photoelectric layer can also be made of organic solar cell materialsbased on conjugated polymer. It can be, for example, conjugatedpolymer/methanofullerene as described in “2.5% Efficient Organic PlasticSolar Cells”, by S. E. Shaheen C. J. Brabec, N. S. Sariciftci, F.Padinger, T. Fromherz, J. C. Hummelen, Applied Physics Letters, vol. 78,no. 6 (2001) 841, or conjugated polymer/conjugated polymer, conjugatedpolymer/organic molecule, organic molecule/organic molecule, conjugatedpolymer/inorganic oxides, selenides and sulfides, organicmolecule/inorganic oxides, selenides and sulfides.

The photoelectric layer can also be based on carbon nanotubes asdescribed by E. Kymanskis et al. Applied Physics Letters, vol. 80, no. 1(2002) 112, or nanowires, preferably carbon nanotubes or metal oxidenanotubes.

The efficiency of these materials used as solar cells is relatively lowdue to the broad solar spectrum. However the invention is related tofuture generation of optical storage, which will make use of relativeshort wavelength, such as 405 nm for blu-ray disk, where quantumefficiency of up to 60% can be reached using proper dye materials.

A conventional player for reading data carrier does not allow a read outof a data carrier in accordance with the invention as the data areencrypted on said carrier. That is why a device in accordance with theinvention comprises:

means for reading the optical signal 8 delivered by the specific area 4of the information layer 1,

means for reading the electrical signal 9 delivered by the additionallayer 2,

means for computing a cryptographic key from a combination of theoptical signal and the electrical signal, and

means for decrypting the encrypted data contained in the data carrierfrom the cryptographic key.

The means for computing are, for example, adapted to compute acorrelation function of the optical and electrical signals, in order toobtain the cryptographic key.

It is to be noted that such a device is also able to read conventionaldiscs, i.e. discs that are not encrypted. It means that a disc is readas a non-encrypted disc when no cryptographic key is detected.

It is also to be noted that the optical and electrical signals as wellas the cryptographic key can be either digital or analog.

A device for reading such data carriers is consequently adapted toidentify from the associated opto-electrical structure thecharacteristic information present on a data carrier, to derive from itthe cryptographic key, and to decrypt the user-information recorded onthe data carrier.

A recorder attempting to clone an original data carrier, i.e. toduplicate the user-information contained in an original data carrier, aROM disc for example, on a second data carrier will not be able torecord onto the second data carrier also the characteristic information,like the one present on the original data carrier, necessary to decryptthe user-information. As a consequence the user-information contained inthe second data carrier cannot be decrypted and played.

However, the data carrier in accordance with the invention does not needto actually contain user-information, but it can also be a data carrierof recordable type, for example a RW or a R disc. A recorder for such arecordable data carrier will consequently be adapted to identify fromthe associated opto-electrical structure the characteristic information,to use said characteristic information to encrypt accordingly theuser-information to be recorded, and to record the encrypteduser-information.

Any reference sign in the following claims should not be construed aslimiting the claim. It will be obvious that the use of the verb “tocomprise” and its conjugations do not exclude the presence of any othersteps or elements besides those defined in any claim. The word “a” or“an” preceding an element or step does not exclude the presence of aplurality of such elements or steps.

1. A data carrier (10) comprising: an information layer (1) comprising aspecific area (4) able to deliver a first optical signal (8) and asecond optical signal when illuminated by a light source, a patternedadditional layer (2) able to deliver an electrical signal (9) whenilluminated by the second optical signal, said electrical signalcorresponding to a predetermined pattern, the combination of the firstoptical signal (8) and of the electrical signal (9) forming acryptographic key that is required to decrypt encrypted data containedin the information layer (1).
 2. A data carrier as claimed in claim 1,wherein the predetermined pattern is obtained from a segmentation of theadditional layer (2) in activated (2 a) and deactivated (2 b) areas. 3.A data carrier as claimed in claim 1, wherein the additional layer (2)comprises electrodes (5,6), one of which being segmented (6 a,6 b) inorder to obtain the predetermined pattern.
 4. A data carrier as claimedin claim 1, wherein the specific area (4) is contained in theinitialization area of the information layer (1).
 5. A data carrier asclaimed in claim 1, wherein the additional layer (2) is a thermoelectriclayer.
 6. A data carrier as claimed in claim 1, wherein the additionallayer (2) is a photoelectric layer.
 7. A data carrier as claimed inclaim 6, wherein the photoelectric layer (2) is made of amorphoussilicon.
 8. A data carrier as claimed in claim 6, wherein thephotoelectric layer (2) is made of photoelectric tungsten disulfide. 9.A device for reading a data carrier as claimed in claim 1, said devicecomprising: means for reading the first optical signal (8) delivered bythe specific area (4) of the information layer (1), means for readingthe electrical signal (9) delivered by the additional layer (2), meansfor computing a cryptographic key from a combination of the firstoptical signal (8) and the electrical signal (9), and means fordecrypting encrypted data contained in the data carrier from thecryptographic key.
 10. A method of reading a data carrier as claimed inclaim 1, said method comprising the steps of: reading the first opticalsignal (8) delivered by the specific area (4) of the information layer(1), reading the electrical signal (9) delivered by the additional layer(2), computing a cryptographic key from a combination of the firstoptical signal (8) and the electrical signal (9), and decryptingencrypted data contained in the data carrier from the cryptographic key.11. A device for recording information on a data carrier as claimed inclaim 1, said device comprising: means for reading the first opticalsignal (8) delivered by the specific area (4) of the information layer(1), means for reading the electrical signal (9) delivered by theadditional layer (2), means for computing a cryptographic key from acombination of the first optical signal (8) and the electrical signal(9), means for encrypting information based on the cryptographic key,and means for storing the encrypted information on the data carrier. 12.A method of recording information on a data carrier as claimed in claim1, said method comprising the steps of: reading the first optical signal(8) delivered by the specific area (4) of the information layer (1),reading the electrical signal (9) delivered by the additional layer (2),computing a cryptographic key from a combination of the first opticalsignal (8) and the electrical signal (9), encrypting information basedon the cryptographic key, and storing the encrypted information on thedata carrier.